Sand holes in the middle of the machined die steel?

In some large parts of mould steel processing, it will be found that there are sand holes in the centre, which often brings a very bad impact on the quality of the product, so what is the reason for the sand holes in the middle of the mould steel?

Generally speaking, most of the sand holes appear in mould steel are modules, which are problems with the forging of modules, which may be inadequate forging, or problems with the previous casting process. Rolling flat, on the other hand, is generally not a problem.

Some experienced die steel people believe that due to the initial billet centre has shrinkage loose, or forging process in the temperature below the final forging temperature also continue to forging caused by the core organization to produce cracks. If there is a large hole in the centre of the die can be machined out of the past 80-90's, the steel mill Cr12MoV round steel, the core often have this problem.